CA1329251C - Optical fibre measuring device, gyrometer, central navigation and stabilizing system - Google Patents
Optical fibre measuring device, gyrometer, central navigation and stabilizing systemInfo
- Publication number
- CA1329251C CA1329251C CA000611296A CA611296A CA1329251C CA 1329251 C CA1329251 C CA 1329251C CA 000611296 A CA000611296 A CA 000611296A CA 611296 A CA611296 A CA 611296A CA 1329251 C CA1329251 C CA 1329251C
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- analog
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- G01C19/72—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers
- G01C19/726—Phase nulling gyrometers, i.e. compensating the Sagnac phase shift in a closed loop system
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Power Engineering (AREA)
- Radar, Positioning & Navigation (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Remote Sensing (AREA)
- Gyroscopes (AREA)
- Measuring Magnetic Variables (AREA)
- Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
- Measurement Of Current Or Voltage (AREA)
- Tests Of Electronic Circuits (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
OPTICAL FIBRE MEASURING DEVICE, GYROMETER, CENTRAL
NAVIGATION AND STABILIZING SYSTEM
The invention relates to an optical-fibre mea-suring device of the type in which the variation of a parameter causes a difference of progression.
Such a device permits the measurement of speed of rotation or of current and of magnetic field.
This device comprises electronic means effect-ing a digital processing of the signal and optimizing its performance levels. It comprises:
- an analog-digital converter (11), - a digital processing system (12), - a control loop digital filter (13), - a register (14) supplying a signal which is a function of the measured parameter, - an accumulator (15), - a digital-analog converter (16).
Figure 2
OPTICAL FIBRE MEASURING DEVICE, GYROMETER, CENTRAL
NAVIGATION AND STABILIZING SYSTEM
The invention relates to an optical-fibre mea-suring device of the type in which the variation of a parameter causes a difference of progression.
Such a device permits the measurement of speed of rotation or of current and of magnetic field.
This device comprises electronic means effect-ing a digital processing of the signal and optimizing its performance levels. It comprises:
- an analog-digital converter (11), - a digital processing system (12), - a control loop digital filter (13), - a register (14) supplying a signal which is a function of the measured parameter, - an accumulator (15), - a digital-analog converter (16).
Figure 2
Description
2 13 2 9 2 ~1 OPTICAL-FIBRE MEASURING DEVICE, GYROMETER, BACKGROUND OF THE INVENTION
The invention relates to an optical-fibre mea-suring device permitting the measurement of the variation of a parameter which produces non-reciProcal disturbances in a SAGNAC ring interferometer.
The SAGNAC interferometer and the Physical phe-nomena which it utilizes are well known. In such an interferometer, a beam sPlitter or some other separating device divides an incident wave. The two oppositelY
propagating waves thus created propagate in opposite directions along a closed optical Path, recombine and generate interferences which are dependent uPon the phase shift of the waves in the course of their recombination.
Originally, the closed oPtical path of the SAGNAC interferometers was defined by mirrors. It is now known that it can be formed bY a multi-turn coil of monomode oPtical fibre.
lt is likewise known that certain physical phe-nomena are capable of producing disturbances, particu-larly Phase shifts, which are non-reciprocal, on the oppositely Propagating waves giving rise to a relative phase shift of these waves which modify their state of interference in the course of their recombination.
The measurement of this relative Phase shift permits the quantification of the physical phenomenon which has given rise to it.
The principal physical phenomenon capable of creating these non-reciprocal disturbances i9 the SAGNAC
~ effect produced bY the rotation of the interferometer in - relation to an axis Perpendicular to the plane of its closed optical path. The FARADAY effect, or collinear magneto-optical effect, is likewise known as producing non-reciprocal effects of this tYpe. This has, for . ~
,, .
:. ~ . . ..
: . .
~3~9251 example, been described in an article in the journal Optic Letters (Vol. 7, No. 4, April 1982, pages 1~0-182) by K. BoHM. Under certain conditions, other effects may likewise produce a non-reciprocal phase shift.
On the other hand, the variations of numerous parameters representing the environment which frequently give rise to disturbances of the measurements have only reciprocal effects on the SAGNAC interferometer, do not disturb the relative Phase shift between the oppositely propagating waves and therefore have no influence on the measurement of the parameter under investigation. This is 50 in the case of slow variations of temperature, of indices etc.... which modifY the optical Path traversed by the waves, but modify it in a reciprocal manner.
lS Numerous Projects have been undertaken for the purpose of imProving the sensitivitY and the precision of the measurements which can be made with such a measuring apparatus. It will be possible, for example, to consult the document GB 2 152 207 and the publication Electronics Letters (Vol. 19 No. 23, November 1983 Pages 997-999, an article bY K. BoHM).
ln Particular, it has first of all been found that the response provided bY the SAGNAC interferometer is of the form P = Po(1 + cos. a~ ) and thus that the sensitivity of this signal close to the phase difference 0 is low. It has been proposed to introduce a ~, phase difference modulation, squared with an amPlitude of plus or minus ~/2 for examPle, which displaces the operating Point and produces a periodic signal, the amplitude of which i~ a sinusoidal function of the measured Parameter and which it is therefore possible to use with a greater sensitivity and stability.
It was then shown that the precision of the measurement is improved bY the use of a zero method which is likewise referred to as closed-loop oPeration.
According to this method, a suPplement~rY Phase shift referred to as a feedback phase shift ~-~ is aPplied and :
,, . . , -:, ~
; .
. :,:
:- ~
4 13~9~5~
serves to compensate the phase shift A~ produced by the measured parameter. The sum of these two phase shifts~-~
and ~ is maintained at zero; this permits the interferometer to be operated with the maximum Precision~
The measurement is made bY use of the signal required for the production of the feedback phase shift Thus, the measurement is stable and linear.
The control may be produced by generating phase progressions of a height ~ at each time T~ T being the proPagation time in the coil, the phase modulator or modulators being Placed at the ends of the coil.
The EurGpean P~tent EP 0,168,292 describes such a measuring system. Accor,ding to the device which it proposes, the signal produced by variation of the mea-sured parameter Produces a variation of the output signal of the detector. The amplitude of this variation is extracted by circuits for analog sYnchronous detection which, after analog processing by a DIP (differential, integral, proPortional) filter, conventionally ensures the stability of the control loop. An analog-digital converter gives the digital value of the progression ~ which has been i~troduced in order to ensure the compensation, and there are added a control signal generator, the purpo~e of which is to formulate a digital ramp in steps, and finallY a digital-analog converter which generates the drive signal returning from the phase modulator, on the basis of this ramp.
In seeking a maximum sensitivity and precision of the measurement, the devices of the prior art exhibit certain disadvantages:
. ~n analog synchronous detection (also re-ferred to as demodulation) generally involves a zero drift at the output which is reflected in an error in the measurement.
. The analog-digital converter required to con-struct this device must be able to Process the comPen-sation phase shift directly. It must include a number of 1~9251 bits linked to the maximum amplitude of the signal at its input; this leads, in practice, in order that it should not limit the precision of the measurement, to an analog-digital converter including a number of bits of the order of 18.
SUMMARY OF THE INVENTION
The object of the Present invention is there-fore to improve the precision and the sensitivitY of a measuring device based on a SAGNAC ring interferometer incorporating a monomode optical fibre, It is likewise an object in such a measuring device to overcome any pos~ible zero drifts.
It is a further object of the Present invention to permit the obtaining of a measurement of quality equal to or greater than that available by the device of the Prior art with a less ~ophisticated analog-digital converter.
In order to achieve these objects, the subiect of the invention is an oPtical-fibre measuring device of the type in which the variation of a parameter causes a difference of phase, comprising a quasi-monochromatic light source, a SAGNAC ring interferometer incorPorating a monomode oPtical fibre, a detector, a phase modulator, a polarizer and a spatial filter which are placed between the source and the interferometer, electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of the demodulated error signal as a function of the difference of Phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase i5 maintained at zero, and supplying, by utilizing the control signal of the modulator, a signal which is a function of the variation of the measured parameter.
In ~uch a device, it is proposed that the said - electronic means comPriSe an analog-digital converter , 1~2~2~1 intended to digitalize the signal originating from the detector, a digital processing system utilizing the signal suPplied bY the analog-digital converter and re-ducing its component to the frequency of the modulation around the continuous (dc), a control loop digital filter supplied by the signal emerging from the digital processing system, supplying a signal representing the measured parameter, a register receiving the signal emerging from the control loop digital filter and ~upplying ~ signal which is a function of the measured parameter for any desired external use, an ~ccumulator supPlied by the signal emerging from the regi~ter, generating a digital ramP~ the sloPe of which i8 a function of the measured rotation, a digital-analog converter supplied bY the feedback signal th~t can be a ramp emanating from the accumulator and controlling the phase modulator.
The subject of the invention is also a gyrometer in accordance with the measuring device defined hereinabove in which the measured parameter i3 the speed of rotation of the interferometer about its axis.
The subject of the invention is furthermore a central inertial stabilization or navigation system comprising at least one gyrometer as defined hereinabove.
~RIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood on readin~ the description which will follow, which i5 given with reference to the drawings, in which:
. Figure 1 is a known measuring device based on a SAGNAC ring interferometer.
. Figure 2 represents the electronic means for the digital Processins of the signal according to the invention.
. Figure 3 represents the analog modulation signal resulting after conversion from the digital '(~
addition of the feedback signal in the particular case of a ramP and of the squared modulation.
The optical-fibre measuring device of the in-vention comprises a quasi-monochromatic light source which is most frequentlY a laser or a super luminescent diode, and a SAGNAC ring interferometer incorPoratins a monomode optical fibre, which interferometer is desig-nated overall by the reference 2.
This ring interferometer 2 comprises a beam sPlitter 3 ensuring the separation of the waves at the entrance of the interferometer, and then their recombi-nation at the exit, and a closed optical path 4 consis-ting of a monomode oPtical fibre wound uP on itself.
This measuring device further comprises a de-tector 5 suPPlying a signal which is a function of the state of interference of the waves at the exit of the interferometer itself.
The oPtical signal is supplied to the detector 5 via a beam splitter 6, for examPle consisting of a semi-transparent Plate.
The interferometer is adiusted in such a manner that the waves are parallel in the course of their re-combination, the signal suPPlied by the detector thus being a function of the phase shift between these two waves.
On the optical path of the interferometer there is interposed a modulator 7 which, being controlled on the basis of an electrical signal, is capable of intro-ducing a given phase shift of the two waves. The operation of the interferometer is improved bY inter-: posing between the light source 1 and the entrance of the ring, that is to say the beam sPlitter 3, a polarizer 8 and a spatial filter 9. This spatial filter is compo~ed of a monomode oPtical fibre.
In the text which follows, we shall use without distinction the terms "phase shift" and "difference of 8 13292~1 phase" to de~ignate the physical effects produced in the interferometer.
Electronic means 10 control in feedback the phase modulator 7, as a function of the signal received from the detector 5.
These electronic means 10 are designed in such a manner that, on the one hand, the variation of the demodulated error signal as a function of the difference of progression produced between the two waves close to the zero is sinusoidal. This arrangement permits a verY
good sensitivity of the variation of the demodulated error signal close to the zero of the difference of progression to be obtain,ed, while it can easi 1Y be understoo~ that, when the dependency of the signal in ~ 15 relation to the difference of phase is of cosinusoidal '~ form, the sensitivity close to the zero of the difference ~;, of phase is very low.
v On the other hand, the function of these elec-tronic means 10 is to maintain the difference of phase at zero. That is to say that, when the variation of the - measured Parameter introduces a Phase shift between the ; two waves in the interferometer, this Phase shift `~ produces a variation of the signal emitted by the detector S involving, via the electronic means 10 and the phase modulator 7, an action equal and of opposite direction to the Phase shift initially Produced in such a .. manner that the total Phase shift is reduced to the value:~ O.
Finally, these electronic means 10 suPPly, bY
use of the control signal of the phase modulator 7, a signal which is a function of the variation of the mea-sured parameter.
According to the invention, the electronic means 10 comprise an analog-digital converter 11 intended to digitalize the signal emitted by the detector. The digital signal emanating from this analog-digital converter is transmitted to a digital processing system :
., . ~ .
, 132~251 12 utilizing this signal and reducing its comPonent to the frequencY of modulation around the continuous in such a manner as to extract the genuinelY significant signal.
It is a significant element of the invention to carry out S the digitalization of the signal at the outPut of the detector before carrying out its digital processing.
The electronic means 10 comprise a control looP
digital filter 13 which is suPplied bY the low signal emerging from the digital Processing system which ensures an operation with low error, low response time and good stability of the control. This may be a digital accumulator. This filter 13 supplies a signal representing the measured parameter.
The electronic means 10 comprise a register 14 receiving the signal emerging from the digital filter 13 supplying a signal which is a function of the measured parameter for any desired external use.
An accumulator (15) supplied by the signal emerging from the register (14) generates a feedback signal which is a function of the measured parameter.
Preferably, the feedback signal is a digital ` ramp 17, the slope of which is a function of the measured parameter. After addition of a modulation bY the digital adder 18, a digital-analog converter 16 suPplied bY the ramp signal 17 emanating from the accumulator 15 controls the Phase modulator 7.
The operation of the measuring device of the invention is the following: when the measured parameter is stable, the electronic control means 10 introduce, via the phase modulator 7, a constant amPlitude modulation of - the Phase shift between the oppositely propagating waves within the ring 4. The detector 5 thus produces a modulated signal which is digitalized bY the converter 11 and then processed by the digital processing system 12, which supplies a zero signal to the accumulator 15 maintaining the register 14 at a constant value: this maintains the ramp 17 in its condition and thus maintains i:
~ .,.
" :
13292~1 the signal supplied to the modulator 7. It is thus verified that this condition is stable.
In the course of a variation of the measured parameter, a constant phase shift is superposed on the periodic phase shift corresponding to the st~ble condi-tion between the oppositely Propasatins waves at the location of the ring 4. The signal then supplied by the detector 5 after digitalization bY the sampler 11 and processins by the disital processing system 12 thus has a level different from zero which produces a supPlY at the location of the accumulator 15 and a variation of the parameter register 14. This variation involves a modification of the ramp generated at the location 15 and thus of the phase shift introduced bY the modulator 7, thus reducing the phase shift between the oppositely propagating waves at the output of the ring 4 to a zero value with the exception of the Periodic modulation mentioned hereinabove.
It is thus understood that the samPling pro-posed according to the invention before the digital ; Processins is apPlied to a signal which is a function of - the variation of the measured parameter and not of the absolute value of this parameter. This permits the utilization of a sampler processing a number of bits which is limited, for example 8, while still maintaining the precision and the quality of the measurement.
,', According to a Preferred embodiment, the digi-, tal processing system 12 of the invention cl~ssifies alternately the digitalized samPles in two classes, of which it forms the digital mean values, which it then compares in order to deduce the error signal therefrom.
-` This arrangment permits the avoidance of the effects of a possible zero drift. Such an arrangement is made Possible by the digitalization of the signal before its digital processing.
The neutralization of this drift is all the more important as in this tYPe of measuring aPParatus ~ .
.: ~
there is frequently performed an integration of the measured Parameter over a long period which is very sensitive to the zero drifts.
Figure 3 shows the digital addition of the ramP
and of the squared modulation 17 which makes uP the ex-citation signal formulated bY the electronic means 10 in order to control the phase modulator 7, in a condition in which the measured parameter is constant. On this graph, time is rePresented as abscissa and the phase shift as ordinate. The value of the measured parameter is a function of the phase shift existing between two successive Periods of the squared function. The right hand part of this graph rePresents the phenomena known per se which take place in the course of overflow of a ; 15 register used in the course of the generation of the ramP, According to a preferred embodiment, the mea-suring device of the invention is characterized in that the sampler oPerates at an aPproximate frequencY of 1 MHz for a fibre length equal to approximately 200 m.
Under such conditions, the device of the inven-tion which Permits the reduction of the sampling dynamics permits the use of a, for examPle, 8-bit analog-digital converter, while the register 14 containing the value of -~ 25 the measured parameter ensures a Precision corresPonding to its size which is of aPProximately 17 to 26 bits.
The construction of a register of this size rePresents onlY a slight constraint since, in wired logic, it can be obtained with a plurality of adders, for example parallel 8-bit adders.
The measuring device of the invention is Par-ticularly well suited to the construction of a gYrometer.
In this case, the measured parameter is the sPeed of ~; rotation of the interferometer about its axis.
This gyrometer is advantageouslY included in the construction of inertial stabilization or navigation ;~ -control systems.
, .
'' '~
. .
, :
12 1 ~ 29 2 Such an arrangement is likewise verY well suited to the construction of the device for me~suring magnetic fields and electric current utilizing the FARADAY effect.
:, .
.
' ' ~ , : , ,
The invention relates to an optical-fibre mea-suring device permitting the measurement of the variation of a parameter which produces non-reciProcal disturbances in a SAGNAC ring interferometer.
The SAGNAC interferometer and the Physical phe-nomena which it utilizes are well known. In such an interferometer, a beam sPlitter or some other separating device divides an incident wave. The two oppositelY
propagating waves thus created propagate in opposite directions along a closed optical Path, recombine and generate interferences which are dependent uPon the phase shift of the waves in the course of their recombination.
Originally, the closed oPtical path of the SAGNAC interferometers was defined by mirrors. It is now known that it can be formed bY a multi-turn coil of monomode oPtical fibre.
lt is likewise known that certain physical phe-nomena are capable of producing disturbances, particu-larly Phase shifts, which are non-reciprocal, on the oppositely Propagating waves giving rise to a relative phase shift of these waves which modify their state of interference in the course of their recombination.
The measurement of this relative Phase shift permits the quantification of the physical phenomenon which has given rise to it.
The principal physical phenomenon capable of creating these non-reciprocal disturbances i9 the SAGNAC
~ effect produced bY the rotation of the interferometer in - relation to an axis Perpendicular to the plane of its closed optical path. The FARADAY effect, or collinear magneto-optical effect, is likewise known as producing non-reciprocal effects of this tYpe. This has, for . ~
,, .
:. ~ . . ..
: . .
~3~9251 example, been described in an article in the journal Optic Letters (Vol. 7, No. 4, April 1982, pages 1~0-182) by K. BoHM. Under certain conditions, other effects may likewise produce a non-reciprocal phase shift.
On the other hand, the variations of numerous parameters representing the environment which frequently give rise to disturbances of the measurements have only reciprocal effects on the SAGNAC interferometer, do not disturb the relative Phase shift between the oppositely propagating waves and therefore have no influence on the measurement of the parameter under investigation. This is 50 in the case of slow variations of temperature, of indices etc.... which modifY the optical Path traversed by the waves, but modify it in a reciprocal manner.
lS Numerous Projects have been undertaken for the purpose of imProving the sensitivitY and the precision of the measurements which can be made with such a measuring apparatus. It will be possible, for example, to consult the document GB 2 152 207 and the publication Electronics Letters (Vol. 19 No. 23, November 1983 Pages 997-999, an article bY K. BoHM).
ln Particular, it has first of all been found that the response provided bY the SAGNAC interferometer is of the form P = Po(1 + cos. a~ ) and thus that the sensitivity of this signal close to the phase difference 0 is low. It has been proposed to introduce a ~, phase difference modulation, squared with an amPlitude of plus or minus ~/2 for examPle, which displaces the operating Point and produces a periodic signal, the amplitude of which i~ a sinusoidal function of the measured Parameter and which it is therefore possible to use with a greater sensitivity and stability.
It was then shown that the precision of the measurement is improved bY the use of a zero method which is likewise referred to as closed-loop oPeration.
According to this method, a suPplement~rY Phase shift referred to as a feedback phase shift ~-~ is aPplied and :
,, . . , -:, ~
; .
. :,:
:- ~
4 13~9~5~
serves to compensate the phase shift A~ produced by the measured parameter. The sum of these two phase shifts~-~
and ~ is maintained at zero; this permits the interferometer to be operated with the maximum Precision~
The measurement is made bY use of the signal required for the production of the feedback phase shift Thus, the measurement is stable and linear.
The control may be produced by generating phase progressions of a height ~ at each time T~ T being the proPagation time in the coil, the phase modulator or modulators being Placed at the ends of the coil.
The EurGpean P~tent EP 0,168,292 describes such a measuring system. Accor,ding to the device which it proposes, the signal produced by variation of the mea-sured parameter Produces a variation of the output signal of the detector. The amplitude of this variation is extracted by circuits for analog sYnchronous detection which, after analog processing by a DIP (differential, integral, proPortional) filter, conventionally ensures the stability of the control loop. An analog-digital converter gives the digital value of the progression ~ which has been i~troduced in order to ensure the compensation, and there are added a control signal generator, the purpo~e of which is to formulate a digital ramp in steps, and finallY a digital-analog converter which generates the drive signal returning from the phase modulator, on the basis of this ramp.
In seeking a maximum sensitivity and precision of the measurement, the devices of the prior art exhibit certain disadvantages:
. ~n analog synchronous detection (also re-ferred to as demodulation) generally involves a zero drift at the output which is reflected in an error in the measurement.
. The analog-digital converter required to con-struct this device must be able to Process the comPen-sation phase shift directly. It must include a number of 1~9251 bits linked to the maximum amplitude of the signal at its input; this leads, in practice, in order that it should not limit the precision of the measurement, to an analog-digital converter including a number of bits of the order of 18.
SUMMARY OF THE INVENTION
The object of the Present invention is there-fore to improve the precision and the sensitivitY of a measuring device based on a SAGNAC ring interferometer incorporating a monomode optical fibre, It is likewise an object in such a measuring device to overcome any pos~ible zero drifts.
It is a further object of the Present invention to permit the obtaining of a measurement of quality equal to or greater than that available by the device of the Prior art with a less ~ophisticated analog-digital converter.
In order to achieve these objects, the subiect of the invention is an oPtical-fibre measuring device of the type in which the variation of a parameter causes a difference of phase, comprising a quasi-monochromatic light source, a SAGNAC ring interferometer incorPorating a monomode oPtical fibre, a detector, a phase modulator, a polarizer and a spatial filter which are placed between the source and the interferometer, electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of the demodulated error signal as a function of the difference of Phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase i5 maintained at zero, and supplying, by utilizing the control signal of the modulator, a signal which is a function of the variation of the measured parameter.
In ~uch a device, it is proposed that the said - electronic means comPriSe an analog-digital converter , 1~2~2~1 intended to digitalize the signal originating from the detector, a digital processing system utilizing the signal suPplied bY the analog-digital converter and re-ducing its component to the frequency of the modulation around the continuous (dc), a control loop digital filter supplied by the signal emerging from the digital processing system, supplying a signal representing the measured parameter, a register receiving the signal emerging from the control loop digital filter and ~upplying ~ signal which is a function of the measured parameter for any desired external use, an ~ccumulator supPlied by the signal emerging from the regi~ter, generating a digital ramP~ the sloPe of which i8 a function of the measured rotation, a digital-analog converter supplied bY the feedback signal th~t can be a ramp emanating from the accumulator and controlling the phase modulator.
The subject of the invention is also a gyrometer in accordance with the measuring device defined hereinabove in which the measured parameter i3 the speed of rotation of the interferometer about its axis.
The subject of the invention is furthermore a central inertial stabilization or navigation system comprising at least one gyrometer as defined hereinabove.
~RIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood on readin~ the description which will follow, which i5 given with reference to the drawings, in which:
. Figure 1 is a known measuring device based on a SAGNAC ring interferometer.
. Figure 2 represents the electronic means for the digital Processins of the signal according to the invention.
. Figure 3 represents the analog modulation signal resulting after conversion from the digital '(~
addition of the feedback signal in the particular case of a ramP and of the squared modulation.
The optical-fibre measuring device of the in-vention comprises a quasi-monochromatic light source which is most frequentlY a laser or a super luminescent diode, and a SAGNAC ring interferometer incorPoratins a monomode optical fibre, which interferometer is desig-nated overall by the reference 2.
This ring interferometer 2 comprises a beam sPlitter 3 ensuring the separation of the waves at the entrance of the interferometer, and then their recombi-nation at the exit, and a closed optical path 4 consis-ting of a monomode oPtical fibre wound uP on itself.
This measuring device further comprises a de-tector 5 suPPlying a signal which is a function of the state of interference of the waves at the exit of the interferometer itself.
The oPtical signal is supplied to the detector 5 via a beam splitter 6, for examPle consisting of a semi-transparent Plate.
The interferometer is adiusted in such a manner that the waves are parallel in the course of their re-combination, the signal suPPlied by the detector thus being a function of the phase shift between these two waves.
On the optical path of the interferometer there is interposed a modulator 7 which, being controlled on the basis of an electrical signal, is capable of intro-ducing a given phase shift of the two waves. The operation of the interferometer is improved bY inter-: posing between the light source 1 and the entrance of the ring, that is to say the beam sPlitter 3, a polarizer 8 and a spatial filter 9. This spatial filter is compo~ed of a monomode oPtical fibre.
In the text which follows, we shall use without distinction the terms "phase shift" and "difference of 8 13292~1 phase" to de~ignate the physical effects produced in the interferometer.
Electronic means 10 control in feedback the phase modulator 7, as a function of the signal received from the detector 5.
These electronic means 10 are designed in such a manner that, on the one hand, the variation of the demodulated error signal as a function of the difference of progression produced between the two waves close to the zero is sinusoidal. This arrangement permits a verY
good sensitivity of the variation of the demodulated error signal close to the zero of the difference of progression to be obtain,ed, while it can easi 1Y be understoo~ that, when the dependency of the signal in ~ 15 relation to the difference of phase is of cosinusoidal '~ form, the sensitivity close to the zero of the difference ~;, of phase is very low.
v On the other hand, the function of these elec-tronic means 10 is to maintain the difference of phase at zero. That is to say that, when the variation of the - measured Parameter introduces a Phase shift between the ; two waves in the interferometer, this Phase shift `~ produces a variation of the signal emitted by the detector S involving, via the electronic means 10 and the phase modulator 7, an action equal and of opposite direction to the Phase shift initially Produced in such a .. manner that the total Phase shift is reduced to the value:~ O.
Finally, these electronic means 10 suPPly, bY
use of the control signal of the phase modulator 7, a signal which is a function of the variation of the mea-sured parameter.
According to the invention, the electronic means 10 comprise an analog-digital converter 11 intended to digitalize the signal emitted by the detector. The digital signal emanating from this analog-digital converter is transmitted to a digital processing system :
., . ~ .
, 132~251 12 utilizing this signal and reducing its comPonent to the frequencY of modulation around the continuous in such a manner as to extract the genuinelY significant signal.
It is a significant element of the invention to carry out S the digitalization of the signal at the outPut of the detector before carrying out its digital processing.
The electronic means 10 comprise a control looP
digital filter 13 which is suPplied bY the low signal emerging from the digital Processing system which ensures an operation with low error, low response time and good stability of the control. This may be a digital accumulator. This filter 13 supplies a signal representing the measured parameter.
The electronic means 10 comprise a register 14 receiving the signal emerging from the digital filter 13 supplying a signal which is a function of the measured parameter for any desired external use.
An accumulator (15) supplied by the signal emerging from the register (14) generates a feedback signal which is a function of the measured parameter.
Preferably, the feedback signal is a digital ` ramp 17, the slope of which is a function of the measured parameter. After addition of a modulation bY the digital adder 18, a digital-analog converter 16 suPplied bY the ramp signal 17 emanating from the accumulator 15 controls the Phase modulator 7.
The operation of the measuring device of the invention is the following: when the measured parameter is stable, the electronic control means 10 introduce, via the phase modulator 7, a constant amPlitude modulation of - the Phase shift between the oppositely propagating waves within the ring 4. The detector 5 thus produces a modulated signal which is digitalized bY the converter 11 and then processed by the digital processing system 12, which supplies a zero signal to the accumulator 15 maintaining the register 14 at a constant value: this maintains the ramp 17 in its condition and thus maintains i:
~ .,.
" :
13292~1 the signal supplied to the modulator 7. It is thus verified that this condition is stable.
In the course of a variation of the measured parameter, a constant phase shift is superposed on the periodic phase shift corresponding to the st~ble condi-tion between the oppositely Propasatins waves at the location of the ring 4. The signal then supplied by the detector 5 after digitalization bY the sampler 11 and processins by the disital processing system 12 thus has a level different from zero which produces a supPlY at the location of the accumulator 15 and a variation of the parameter register 14. This variation involves a modification of the ramp generated at the location 15 and thus of the phase shift introduced bY the modulator 7, thus reducing the phase shift between the oppositely propagating waves at the output of the ring 4 to a zero value with the exception of the Periodic modulation mentioned hereinabove.
It is thus understood that the samPling pro-posed according to the invention before the digital ; Processins is apPlied to a signal which is a function of - the variation of the measured parameter and not of the absolute value of this parameter. This permits the utilization of a sampler processing a number of bits which is limited, for example 8, while still maintaining the precision and the quality of the measurement.
,', According to a Preferred embodiment, the digi-, tal processing system 12 of the invention cl~ssifies alternately the digitalized samPles in two classes, of which it forms the digital mean values, which it then compares in order to deduce the error signal therefrom.
-` This arrangment permits the avoidance of the effects of a possible zero drift. Such an arrangement is made Possible by the digitalization of the signal before its digital processing.
The neutralization of this drift is all the more important as in this tYPe of measuring aPParatus ~ .
.: ~
there is frequently performed an integration of the measured Parameter over a long period which is very sensitive to the zero drifts.
Figure 3 shows the digital addition of the ramP
and of the squared modulation 17 which makes uP the ex-citation signal formulated bY the electronic means 10 in order to control the phase modulator 7, in a condition in which the measured parameter is constant. On this graph, time is rePresented as abscissa and the phase shift as ordinate. The value of the measured parameter is a function of the phase shift existing between two successive Periods of the squared function. The right hand part of this graph rePresents the phenomena known per se which take place in the course of overflow of a ; 15 register used in the course of the generation of the ramP, According to a preferred embodiment, the mea-suring device of the invention is characterized in that the sampler oPerates at an aPproximate frequencY of 1 MHz for a fibre length equal to approximately 200 m.
Under such conditions, the device of the inven-tion which Permits the reduction of the sampling dynamics permits the use of a, for examPle, 8-bit analog-digital converter, while the register 14 containing the value of -~ 25 the measured parameter ensures a Precision corresPonding to its size which is of aPProximately 17 to 26 bits.
The construction of a register of this size rePresents onlY a slight constraint since, in wired logic, it can be obtained with a plurality of adders, for example parallel 8-bit adders.
The measuring device of the invention is Par-ticularly well suited to the construction of a gYrometer.
In this case, the measured parameter is the sPeed of ~; rotation of the interferometer about its axis.
This gyrometer is advantageouslY included in the construction of inertial stabilization or navigation ;~ -control systems.
, .
'' '~
. .
, :
12 1 ~ 29 2 Such an arrangement is likewise verY well suited to the construction of the device for me~suring magnetic fields and electric current utilizing the FARADAY effect.
:, .
.
' ' ~ , : , ,
Claims (8)
1. Optical-fibre measuring device of the type in which the variation of a parameter causes a difference of phase comprising:
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the variation of the measured parameter, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system utilizing the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing the measured parameter, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of the measured parameter, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder, and controlling the phase modulator.
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the variation of the measured parameter, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system utilizing the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing the measured parameter, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of the measured parameter, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder, and controlling the phase modulator.
2. Measuring device according to claim 1, characterized in that the digital processing system classifies alternately the digitalized samples in two classes, of which it forms the mean values, which it then compares in order to deduce the error signal therefrom.
3. Measuring device according to claim 2, characterized in that the feedback signal is a digital ramp, the slope of which is a function of the measured parameter.
4. Measuring device according to any one of claims 1 to 3, characterized in that the analog-digital converter operates at an approximate frequency of 1 MHz corresponding to a sampling time of 1 µs, in the case of a fibre length equal to approximately 200 m.
5. Measuring device according to claim 1, 2 or 3, characterized in that the register contains from 17 to 26 bits, and in that the analog-digital converter contains from 7 to 9 bits.
6. Optical-fibre gyrometer of the type comprising:
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the speed of rotation of the interferometer about an axis perpendicular to the plane of the ring, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system utilizing the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing speed of rotation, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of speed of rotation, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder and controlling the phase modulator.
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the speed of rotation of the interferometer about an axis perpendicular to the plane of the ring, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system utilizing the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing speed of rotation, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of speed of rotation, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder and controlling the phase modulator.
7. Inertial stabilization or navigation control system comprising at least one optical-fibre gyrometer of the type comprising:
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the speed of rotation of the interferometer about an axis perpendicular to the plane of the ring, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system utilizing the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing speed of rotation, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of speed of rotation, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder and controlling the phase modulator.
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the speed of rotation of the interferometer about an axis perpendicular to the plane of the ring, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system utilizing the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing speed of rotation, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of speed of rotation, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder and controlling the phase modulator.
8. Current and magnetic-field sensor incorporating an optical fibre, in which a variation of difference of progression is produced by the measured parameter by the FARADAY effect, comprising:
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the variation of the measured parameter, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system using the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing the measured parameter, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of the measured parameter, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder and controlling the phase modulator.
- a quasi-monochromatic light source, - a SAGNAC ring interferometer incorporating an optical fibre, - a detector, - a phase modulator, - a polarizer and a spatial filter which are placed between the source and the interferometer, - electronic means controlling in feedback the phase modulator as a function of the signal received from the detector in such a manner that, on the one hand, the variation of a demodulated error signal as a function of the difference of phase close to the zero is sinusoidal, and that, on the other hand, this difference of phase is maintained at zero and supplying, by utilizing the control signal of the modulator, a signal which is a function of the variation of the measured parameter, characterized in that the said electronic means comprise:
- an analog-digital converter intended to digitalize the signal emitted by the detector, - a digital processing system using the signal supplied by the analog-digital converter and reducing its component to the frequency of the modulation around dc, - a control loop digital filter, supplied by the signal emerging from the digital processing system, supplying a signal representing the measured parameter, - a register receiving the signal emerging from the control loop digital filter and supplying a signal which is a function of the measured parameter, - an accumulator supplied by the signal emerging from the register, generating a feedback signal which is a function of the measured parameter, and - a digital-analog converter supplied by the feedback signal emanating from the accumulator after modulation by an adder and controlling the phase modulator.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8811978A FR2636425B1 (en) | 1988-09-14 | 1988-09-14 | FIBER OPTIC MEASUREMENT DEVICE, GYROMETER, NAVIGATION AND STABILIZATION UNIT |
| FR8811978 | 1988-09-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1329251C true CA1329251C (en) | 1994-05-03 |
Family
ID=9369977
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000611296A Expired - Lifetime CA1329251C (en) | 1988-09-14 | 1989-09-13 | Optical fibre measuring device, gyrometer, central navigation and stabilizing system |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0359666B2 (en) |
| JP (1) | JP3078552B2 (en) |
| AT (1) | ATE82800T1 (en) |
| CA (1) | CA1329251C (en) |
| DE (1) | DE68903616T3 (en) |
| ES (1) | ES2036822T5 (en) |
| FR (1) | FR2636425B1 (en) |
| GR (1) | GR3006717T3 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2020379C (en) * | 1989-08-09 | 2001-01-16 | Michael S. Bielas | Digital synthetic serrodyne for fiber optic gyroscope |
| FR2654827B1 (en) * | 1989-11-17 | 1992-03-20 | Photonetics | FIBER OPTIC MEASUREMENT DEVICE, GYROMETER, NAVIGATION AND STABILIZATION UNIT. |
| EP0436052B1 (en) * | 1990-01-03 | 1992-09-23 | LITEF GmbH | Fiber optic sagnac interferometer with digital phase resetting for measuring rotation rate |
| EP0441998B1 (en) * | 1990-02-12 | 1993-06-02 | LITEF GmbH | Fiberoptic sagnac interferometer with digital phase cancellation for measuring rotation rate |
| IT1246572B (en) * | 1991-02-27 | 1994-11-24 | Cise Spa | PROCEDURE AND APPARATUS FOR ABSOLUTE INTERFEROMETRIC MEASUREMENTS OF PHYSICAL SIZES. |
| US5278631A (en) * | 1992-04-24 | 1994-01-11 | Allied Signal Inc. | Closed loop fiber optic gyroscope with signal processing arrangement for improved performance |
| CN105866711B (en) * | 2016-03-22 | 2018-06-19 | 北京信息科技大学 | A kind of method that magnetic field is measured using optical fiber sagnac interferometer |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4299490A (en) * | 1978-12-07 | 1981-11-10 | Mcdonnell Douglas Corporation | Phase nulling optical gyro |
| US4372685A (en) | 1979-01-15 | 1983-02-08 | Max-Planck-Gesellschaft Zur Forderung Der Wissenschaften E.V. | Method and arrangement for the measurement of rotations |
| FR2555739B1 (en) * | 1980-11-07 | 1986-04-04 | Thomson Csf | DEVICE FOR MEASURING A NON-RECIPROCAL PHASE GENERATED IN A RING INTERFEROMETER |
| FR2566133B1 (en) * | 1984-06-14 | 1986-08-29 | Thomson Csf | DEVICE FOR MEASURING A NON-RECIPROCAL PHASE GENERATED IN A RING INTERFEROMETER |
-
1988
- 1988-09-14 FR FR8811978A patent/FR2636425B1/en not_active Expired - Lifetime
-
1989
- 1989-09-13 DE DE68903616T patent/DE68903616T3/en not_active Expired - Lifetime
- 1989-09-13 CA CA000611296A patent/CA1329251C/en not_active Expired - Lifetime
- 1989-09-13 ES ES89402504T patent/ES2036822T5/en not_active Expired - Lifetime
- 1989-09-13 EP EP89402504A patent/EP0359666B2/en not_active Expired - Lifetime
- 1989-09-13 AT AT89402504T patent/ATE82800T1/en not_active IP Right Cessation
- 1989-09-14 JP JP01237421A patent/JP3078552B2/en not_active Expired - Lifetime
-
1992
- 1992-12-30 GR GR920403254T patent/GR3006717T3/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GR3006717T3 (en) | 1993-06-30 |
| EP0359666A1 (en) | 1990-03-21 |
| EP0359666B1 (en) | 1992-11-25 |
| JPH02193013A (en) | 1990-07-30 |
| DE68903616T2 (en) | 1993-06-03 |
| ATE82800T1 (en) | 1992-12-15 |
| ES2036822T3 (en) | 1993-06-01 |
| DE68903616T3 (en) | 1998-02-05 |
| FR2636425B1 (en) | 1990-11-30 |
| JP3078552B2 (en) | 2000-08-21 |
| ES2036822T5 (en) | 1997-10-16 |
| FR2636425A1 (en) | 1990-03-16 |
| EP0359666B2 (en) | 1997-06-25 |
| DE68903616D1 (en) | 1993-01-07 |
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